I have been searching solutions for this problem for a long time.

Motherboard is ASUS P5LD2, graphic card is NVIDIA 6600LE, Hard disk is Hitachi 160GB, RAM is Cossair 2 x 512MB, I am using onboard sound card.

I have tried to go to BIOS to diable the audio driver and re-enable it after system reboot. I also tried to re-install the Realtek HD audio driver inside the motherboard CD. I even went to check if the "windows audio" service is started and in automatic mode. After doing all these, I still cannot get the audio device working. Open the control panel, sound, audio devices, all options under volume are grey and cannot be checked. Under hardware tab, it says that the legacy audio driver is working properly, but the device usage is grey. And this is the same for all the other audio devices.

Can anyone help me solve this problem?

Thanks!

You said "all audio device"? Do you mean you have an extra sound card in there? If so, remove it and try again with only the AC97.

From what you described I can denote that:

1) The drivers are outdated/bad...try newer versions of the drivers from the Asus website.

2)Its possible that your audio in your MOBO is defective
Let's hope that's not the case.

I use onboard sound driver, not a separate one. If my motherboard sound is defective, would it affect if I were to install an external sound card?

No, the external sound cards is normally USB/PCI so it take over. If it don't just disable the onboard.

http://support.asus.com/download/d [...] odel=P5LD2
download the driver from this page
go to control panel-add remove programs and remove any realtek software
go to device manager and if it's still listed there remove it reboot and cancel out of new hardware wizard. disable all ani-virus/anti-spyware programs and third party firewalls install the driver from above site

thanks a million! it really helps!!! Finally got my the sound...

glad we could help and thanks for letting us know how turned out